Plasma engines with a magnetic nozzle, such as the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) Experimental 200 kW spacecraft engine (VX-200), use magnetic fields to constrict and accelerate plasma to produce thrust. Though a majority of plasma particles are expected to escape the magnetic field and there is no experimental evidence of returning ions, a small fraction will follow the magnetic field lines and may impact the spacecraft structure. The fraction returning is expected to be small and this simulation method represents a worse case scenario. Beginning with experimentally determined parameters as conditions in the near field plume of the VX-200, the ion flow field in the far plume and backfield was modeled computationally using particle tracing. It was determined that about 1.2% of the total ion flow, mainly from locations on the fringes of the plume, remains bound by the magnetic field and can impact the engine and radiator panels. The erosion rate on an aluminum (AL 6061) surface is estimated to be very low with 1 micron eroded for roughly every 2 days of engine run time due to this small fraction of trapped ions. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.